package com.ztom.daily.n2022.m4;

/**
 * 统计各位数字都不同的数字个数
 * <p>
 * https://leetcode-cn.com/problems/count-numbers-with-unique-digits/
 *
 * @author ZhangTao
 */
public class Day11CountNumbersWithUniqueDigits {

    public int countNumbersWithUniqueDigits(int n) {
        if (n == 0) {
            return 1;
        }
        if (n == 1) {
            return 10;
        }
        int res = 10;
        int cur = 9;
        for (int i = 0; i < n - 1; i++) {
            cur *= 9 - i;
            res += cur;
        }

        return res;
    }
}
